Treating disease by inhaling medicines has been around for centuries but has advanced and grown considerably since the mid-20th century. Using inhalation therapy to deliver both topically and systemically active drug compounds is increasing as the health-care community recognizes the benefits this route of administration offers to patients. In order for inhalation treatments to be effective, pulmonary delivery devices must enable efficient, safe and consistent delivery of drugs to and through the lungs.
Syringe-based metering systems are well-known in the art of metering systems for their accuracy and simplicity. In a metering system having a rigid syringe/vial system with little or no compressible head space, however, differential thermal expansion and/or contraction can cause net volume change of the fluid contained in the syringe or vial (i.e., a different expansion or contraction between the fluid and the rigid syringe). This volume expansion and/or contraction must be accommodated in the syringe/vial to prevent either an expanding fluid volume from being expressed from the syringe, or a contracting volume from allowing outside air to enter the vial, or creating a low enough vial pressure to cause out-gassing of air or a vapor phase of the liquid in the vial. These volumetric changes can adversely impact metering accuracy.
In addition, metering systems having valves and/or nozzles located downstream of a fluid container outlet typically experience problems with dead volume in the space or passageways fluidly connecting the container outlet and the valves/nozzles. This dead volume can lead to inaccurate and/or inconsistent delivery of fluids. Metering systems having dead volume can be manually primed by the user prior to delivery, however, this requires an extra step for the user. Also, in such manual priming systems, the user may not properly prime the metering system prior to use leading to inaccuracies in fluid delivery.
What is needed are devices, systems, and methods that account for differential thermal expansion/contraction and/or account for dead volume in a metering system to ensure efficient, accurate, and reproducible metered delivery of fluids.